


Something New

by blushingmess



Category: Undertale (Video Game)
Genre: Belly Kink, Gen, Stuffing, Weight Gain
Language: English
Status: In-Progress
Published: 2015-12-23
Updated: 2015-12-23
Packaged: 2018-05-08 17:41:27
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,228
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5506901
Author URL: https://archiveofourown.org/users/blushingmess/pseuds/blushingmess
Summary: <blockquote class="userstuff">
              <p>Sans wakes up to find he's somehow materialized a magic belly during the night. (That's it, that's the plot.)</p>
            </blockquote>





	Something New

**Author's Note:**

> I posted this on tumblr a while back and people liked it, so I figured I might as well upload it here while my slow ass is working on a second chapter.   
> This takes place right before Sans becomes a sentry, so before Frisk shows up.

The first thing Sans notices when he wakes up is that something’s off. Now, he wasn’t expecting to wake up feeling fantastic to begin with. For one, he’s never been a morning person, but lately…

The project he’d been working on with some other scientists had been discontinued a while ago, which he supposes made sense. He can’t remember the last time they’d discovered anything significant. Unfortunately, the lack of daily structure has allowed him to slip into a daily rhythm of doing nothing at all. When your default setting is lazy, it’s pretty hard go out and to do stuff if there’s no-one around to yell at you. With Papyrus spending every one of his many waking hours trying to get Undyne to pay attention to him, Sans’ life has been pretty quiet. As it is, he’s been spending his days going back and forth between his room and Grillby’s, practicing shitty jokes and eating fried garbage.

As much as he hates to admit it, he’s been starting to think Papyrus might have a point about too much grease being bad for him. It should make absolutely no sense, considering skeletons have no digestive system. Never mind the fact that monster food turns into raw magical energy after consumption. But despite all logic, recently he’s been feeling a weird thrumming in his bones that gets worse whenever he eats too much. It’s not exactly an unpleasant feeling, but it does make him feel dizzy and overwhelmed at times, which cannot be good.

So when Sans wakes up after a night of seriously overdoing it with an amount of fries that could probably feed a family, he expects to feel a little worse for wear. But when he rolls out of bed and blindly fumbles around trying to figure out where he discarded his clothes, he’s struck by how clearheaded he is. The thrumming feeling is mostly gone, and now that it’s gone he realises that he never actually noticed how bad it was.

The real surprise comes when he’s putting on his shirt. He’s still partially asleep as he goes through the motions, pulling it over his head, putting his arms through the sleeves, the quiet rattle of his phalanges sliding over his ribs as he pulls his shirt down over the soft slope of his-what?

Now fully awake, Sans’ eyes fly wide open as he takes off his shirt again and looks down to what his hands bumped into a moment ago. Instead of the familiar bones, he finds something in the vibrant blue colour of his own magic connecting the space from his hollow ribcage to his pelvis. Curious and a little alarmed, he reaches down again to gently brush the tips of his fingers against it. It’s warm, and gives a little under the pressure. But that sensation is instantly forgotten about because Sans can also feel his own fingers touching him. It kind of feels like he’s touching one of his own bones, except for the part where it’s nothing like bone at all. He’s stunned by the coldness of his own phalanges that lingers even after he’s reflexively pulled them back. When he touches it again he’s hyper aware of the gentle pressure of his exploring fingers, brushing up and down over the surface, pressing in gently, smoothing over the gradual edge where his hard ribs blend into the softness.

What. The. Hell.

The blue mass puffs out a little and then deflates as he lets out a deep breath. He sits back on his mattress, settling against the wall while he tries to figure things out. It’s a belly. He has a belly. He definitely has a belly, made from his own magic and attached to his own body, and it apparently just decided to magic itself into existence while he was asleep because that’s what magical body parts do, right? No way. From a very young age Sans has always been fully in control of his magic, and even if he wanted to he has no idea how to go about conjuring up an extra body part. If he had, he’d made himself an extra arm to do his job for him while he slept a long time ago. There’s just no way he could accidentally make something like this while he was asleep. Yet… it’s also definitely made from his own magic, he muses while he’s still absently running his hands over it. The colour is a dead giveaway, but there’s a sense familiarity that could never come from a foreign magic, a gently hum he now recognises as the same thrumming he’s been feeling in his bones, only instead of overwhelming it’s now strangely comforting.

When he hears Papyrus stomping around downstairs and shouting his name, he quickly puts on his shirt. He looks down again and sees a gentle curve underneath. It wouldn’t be anything too suspicious… if he weren’t a skeleton. He decides to zip up his hoodie for now as he finishes getting dressed, unlocking his door and opening it to find himself face to face with his own reflection in the chest plate of his brother’s battle body. He looks up to see the fire in his brother’s eyes burning even brighter than usual.  
‘AH, THERE YOU ARE BROTHER. THEY’RE LOOKING FOR TWO NEW SENTRIES NEAR SNOWDIN, AND I TOOK LIBERTY OF SIGNING US BOTH UP!’

—

After spending the rest of his day being literally dragged around by Papyrus, Sans manages to drag himself into Grillby’s and heavily drops down in his usual seat at the bar. He’s extremely worn out, but it’s a different kind of tired than usual. Even though he complained all day, it was great to hang out with his brother. Plus… getting out and being active? He’s never telling Papyrus, but it feels pretty good after sitting around for as long as he has. He orders a burger and a large portion of fries to mentally celebrate, then adds a second burger when he remembers he hasn’t eaten anything today because Papyrus doesn’t take breaks. His stomach growls as he’s waiting for the food to arrive and he’s immediately reminded of why he skipped breakfast as well this morning. His stomach. That is definitely not something his tired mind made up, he confirms as he subtly prods it with a hand that’s still in the pocket of his hoodie.

His thoughts are interrupted by a flaming hand putting his food down in front of him. Sans quickly pulls his hands out of his pockets and gives his thanks to Grillby, then grabs a bottle of ketchup from the counter and douses his fries in it. He can’t help but let out a pleased hum as he swallows down the first couple of fries, the magic energy immediately offering some relief to his hunger. He grabs the first burger and quickly eats most of it in a few big bites, then slowing down to appreciate the flavour before finishing the rest of it. He reaches out for the fries again, then pauses. There’s the usual comforting feeling of new magical energy coursing through his body, but it seems to flow in an entirely different way. Frowning slightly, he slips his left hand back into the pocket of his hoodie. Even through the two layers of fabric, he can feel the warmth radiating off his belly. That’s definitely different from before. Spreading out his fingers, he pushes down a little. This morning his belly had curved out a little, but it feels like it’s bigger now. Huh.

He moves his fingers again, feeling the soft curve and gently grabbing at it, squeezing, jiggling it a little. Being a skeleton, he’s really not used to any part of him being even close to soft. For a moment, Sans is completely lost in thought, eyes wandering around the room until he’s distracted by the light reflecting off of Grillby’s glasses and- oh. Grillby is looking directly at him. Or rather, his face is aimed in Sans’ general direction. It’s pretty difficult to confirm what the exact target of the bartender’s gaze is because he doesn’t actually have eyes, but somehow Sans suspects that if he had eyes they would be aimed at the skeleton unsubtly fondling something inside his pocket. He feels his face flush and looks away, quickly reaching for the ketchup bottle next to him with his right hand and taking a big gulp.

After draining most of the bottle he reaches for the rest of his fries. As he eats them one by one, he’s hyper aware of the magic flowing through him, flowing and swirling before gathering underneath where he still hasn’t removes his left hand from his pocket. The fries are gone far too quickly, and he removes his hand from his pocket to pick up his second burger with both hands. He takes a couple of big bites, accidentally squeezing the burger a little too enthusiastically. He quickly leans forward, trying to make sure the sauce that is now dripping out from all sides ends up on his plate instead of his clothes. He’s mostly successful, if not for the fact that halfway through the movement his belly bumps into the bar, throwing him off so that he ends up with sauce all over his sleeve. Great.

Sans finishes off the last few bites of the burger, holding it with one hand as he uses the other one to rub the upper side of his belly that bumped into the bar. It’s still soft, but a little tighter than before, he notices. Sliding his hand back down towards his pocket, he feels how his stomach is now even rounder than before. He looks down, and while his zipped up hoodie still does a pretty good job concealing it, he can see it push against the zipper a little.

Sans tells Grillby to add the bill to his tab and slides off his seat. As he lands on his feet, he stumbles a little, thrown off by the weight around his middle shifting his centre of balance forward. Straightening his back, he walks towards the door as casually as possible.

—

When Sans gets home, he can hear Papyrus moving around in his bedroom. Sans lets out a quiet sigh of relief. Papyrus is surprisingly observant when he wants to be, and Sans isn’t too eager to try to explain the new addition to his body, especially since he’s not completely sure himself about what’s happening. Papyrus would only worry and fuss over him, when in reality he’s feeling better than he has in quite a while.

That reminds him… he walks up to the fridge, taking a second to consider the contents before grabbing a bottle of soda. He’s not hungry anymore, but as he was walking home, hands in his pockets brushing against his soft sides, jiggling a little with every step… it felt really good. Weird, but good, he muses as he enters his own room and locks the door behind him. He puts down the bottle and takes off his stained hoodie, throwing it in a corner. For the first time since this morning, he gets to take a look at himself. His shirt is getting tight, stretched out where his belly pushes against it. He’s pretty lucky he usually prefers loose clothes, otherwise it would have gotten uncomfortable by now. The waistband of his shorts is cutting into the underside a little, and when he slides his hands under his shirt he notices a slight glow coming out from underneath. Taking off his shirt as well, he finally gets to look down at his belly. It’s emitting a soft glow, and he can see various shades of blue slowly swirling around under the semi-translucent surface.

When he gently presses his hands down, it’s still soft, but there’s a little less give than before. He sits down on his mattress, his back against the wall, in the same spot he found himself in earlier this morning. He bends forward to reach for the soda, his stomach pushing out over the waistband of his shorts and pressing against his femurs. As he leans back again, the bottom of it is still resting on his legs. Sans uncaps the bottle of soda and takes a couple of swigs. Curious, he looks back down at his stomach and he sees a light blue streak of magic, glowing a little brighter than the others. He watches in amazement as it mixes with the rest. He rubs the surface, kneading it a little as he chugs down more soda. It feels really good, but he can’t help but groan when he presses down a little too hard. That’s painful. He eyes the rest of the soda for a second before drinking the rest of it anyway, then immediately regrets it. As he bends forward again to drop the bottle back onto the floor, the press of his femurs into his underbelly is now a little too painful to be comfortable.

Groaning again, Sans drops down onto his back, carefully massaging his round stomach. It’s kind of painful, but there’s also a comfort in the way it pins him against his mattress. The blue mass resonates with his magic with a soft, calming thrum, lulling him into a deep dreamless sleep.


End file.
